I will already tell you, there was no big thing for St. Patrick's Day here. No hangover, no green beer, and that would be unthinkable to do to wine. I also don't think you'd really want to drink naturally green wine. On the positive side, no pinching and no blatant expositions of Irishness. No decorations either though, which was nice. My mother tends to take the holidays a bit overboard. It's reassuring though. Should you ever have a psychotic break, you always know what month it is.
So what I did find amusing is that even though St. Patrick's Day isn't "observed" in the US, they do have saint's Days. In fact, there are lots of saint's days in France. For example, my name although there is no saint who directly bears my name, my name descends from St. Francis of Assisi. So my saint's day is October 4. I am not sure how exactly it's determined though, or if you can choose. That may be something better left to a priest. (It also may be St. Peter if you go off the name which I took when I was confirmed. My mother is catholic and it made her happy, so I did it.) So therefore, you could possibly have people calling you up on your saint's day and wishing you a happy saint's day.
More likely than not though, it's meaningless. People may comment on it, but you don't really get presents. It's more of a trivia thing. I asked my boyfriend when his was, he knew immediately. It's like how we have horoscopes in the US (which France also has) or blood types in Japan. It's not something commonly known or discussed, so don't be surprised if you ask someone and they have no idea when it is.
It's funny though, if you ever get your hair cut in France, you may see a pile of them sitting on the counter where you get it done. Often they are paired with cologne/perfume samples. It's something more for the novelty of having than something to take seriously of course. I have never met anyone who took them seriously or really cared about them though. More of a trivia thing, and it's more common for the older generation to know, or even say something about it to the younger generations.
Just something I thought about today. So Happy Saint Patrick's Day. Who wants to go run some snakes out of some countries?